text:
Why is an accident referred to by flight number instead of registration number of the airframe?
Most accidents are referred to by flight number, for instance MH17 or MH370 to name a few recent ones.
Flight numbers are usually but not always retired after a crash. So why isn't referred to the registration number instead?

Probably because everyone who has ever flown or picked someone up at the airport is familiar with flight numbers, but very few (outside the aviation community) actually realize that planes have a registration number. (Never mind that their car has a registration/plate number - most won't put 2 and 2 together.) A side note, registration numbers can change when the plane changes owners.

For one thing, the flight number is usually shorter and/or easier to remember than the aircraft registration: MH370 vs. 9M-MRO; AF447 vs. F-GZCP

I think one of the reasons is that in case of a accident where there is little hull damage, the registration number might be maintained, leading to a situation where a single registered plane might be part of multiple accidents, leading to confusion. Meanwhile, flight numbers easily get retired and it's far less likely for a flight number to have multiple crashes. the latter is not impossible though: I can find 3 occurences where a flight number has multiple accidents with serious bodycounts.

@user11101: registration numbers are (very obviously) unique too, so that's not a good argument

Most accidents are referred to by flight number

It depends who it is that is referring to the accident, and on who they are addressing.
News media and the general public
Newpapers and other media use flight numbers because that is the number known to friends and relatives of the individuals concerned and because most members of the public who have flown as passengers are very familiar with  the concept of flight numbers but not really familiar with aircraft registration numbers.
Investigators
Investigating authorities have their own numbering schemes for accidents they investigate.
Aircraft registration numbers change when an aircraft is sold to a purchaser based in another country.
The only number that stays with an aircraft for its entire life is the manufacturer's serial number.
All these numbers can appear in official accident investigations reports. The registration number is usually prominent.

AAIB

NTSB

BEA

I think the flight number is more a media thing, like the name of the unfortunate pilot printed everywhere.

Unfortunate or not, at the end of the day, the Captain is responsible for his ship.

@corsiKa: That's not how courts see the thing, responsibility can also be imputed to the manufacturer, the airline, or the ATC, or indeed to the hijacker if there is one. But my comment was more about media sullying pilot's good name before the safety agencies even know the causes. MH370 is a study case. The captain was using a flight simulator at home to land on difficult runways... ooh... very very very suspicious...

The flight number is more readily available than the aircraft's registration number. With a simple call to the departure/arrival airport's information office (or even from the airport's website) anyone can get the flight number.
Sometimes the aircraft is not ready and another one is used for the scheduled flight so the registration number could be difficult to obtain.
Also, a flight number uniquely identifies a route, a departure airport and time, a destination and an airline.

But it's the plane that crashed, not the route. Hence the quesstion.

@DavidRicherby, of course, but it's common to refers to the aircraft flying a certain route .(I mean, even without any accident occurring) using its flight number.

@Richerby: To concerned relatives of passengers, the route crashed, not the plane. You are seeing things from the aviator's point of view, not the passengers'. When releasing information publicly, saying "a plane with registration F-GZCP crashed" doesn't convey any information that I can see, since this information is never given to the public in any other context (the plane can be changed at any time and is not relevant to their itineraries). Saying "Flight AF447 crashed" tells anyone with itinerary information exactly whether they need to be calling the airport or not.

@DavidRicherby Out of interest, if it were a train or a coach that crashed, what would you expect to hear about?

@CptReynolds i would hear it as route number, not the vehicle registration.


text:
What was the inflight entertainment in the early seventies?
In her 1970 song "This Flight Tonight", Joni Mitchell sings

I'm drinking sweet champagne
Got the headphones up high
Can't numb you out
Can't drum you out of my mind
They're playing Goodbye baby, Baby Goodbye
Ooh ooh love is blind

The Sony Walkman first came out near the end of that decade. So what was Joni listening to on that fateful flight?

I will award a 100 point bonus to anyone who can identify the plane she was on in the song based on the lyrics.

Seventies mid-flight entertainment consisted in no small part of this. Yes, the song only strengthens that argument.

What airplane you are referring to?

@Farhan The plane she was on.

@SQB Do you have a picture or video of that song? I couldn't find any.

@Farhan You can follow the link in the question for the lyrics. I don't think there is an official video, but you can hear her sing it here: http://www.youtube.com/watch?v=iTfB8Q6DpZ0

@SQB Actually what I meant to ask is where how do you see the airplane in that song? I already found the song audio on YouTube but that doesn't have a picture of the airplane. Or did I miss it?

@Farhan It was kind of a joke actually, but I thought that perhaps someone would know a crazy little detail like there only being one airline serving champagne on their domestic flights to Las Vegas at that time, only flying one type of airliner.

I thought the air traffic with the pilots was more interesting than any music.

During that time, the in-flight entertainment mostly available on flights was radio1 and/or TVs. Although it was not on all flights. Oops, that is true even today.
The radios may or may not have channels. If they had, there was a knob on the armrest, next to headset jacks, to switch channels. The headsets were pneumatic units like this:

The in-flight movies were shown using one or more common CRT TVs mounted on ceilings or walls and audio could be heard using the headsets. The first time a movie was shown on an international flight was in 1962 by PIA. It was more like the picture below but instead of LCD monitors, there were CRTs.

In mid-seventies, Braniff Airways was the first airline to offer video games in-flight.
By 1979, electronic headsets replaced their pneumatic counterparts, which improved audio quality.

Wikipedia has a detailed article about the history of in-flight entertainment:

In 1971, TRANSCOM developed the 8mm film cassette. Flight attendants
  could now change movies in-flight and add short subject programming.
In the late 1970s and early 1980s, CRT-based projectors began to
  appear on newer widebody aircraft, such as the Boeing 767.

This website has nice slideshow about the history.

1: Not actually a radio, but recorded audio

Whoa! You could get radio at cruising altitude? I imagine radios work kind of like modern cell phone towers, which you can't really get 7 miles in the air.

Actually, getting cell signal 7 miles in the air isn't the problem (it's not a problem 7 miles away from a station on the ground), it's that you're screaming past them at 350-500 miles per hour. Your phone pretty much can't lock on to an antenna, or gets too many, and you get 'no service'

Surely you don't literally mean "radio".  I wouldn't think a plane would stay in range of a commercial FM station for long enough, and I'd think longer-range transmissions would be of unsatisfactorily low quality.  Wouldn't it have been recorded music? Certainly various kinds of audio tape players were available by then.

And as your quote says, there wouldn't have been CRT TVs, like in your picture, by the early 1970s.  A white screen and film projector seems much more likely.

@raptortech97: Radio antennas have to be tuned down at night because the range is just too big. It's entirely the opposite of cell towers. Curvature of the earth starts to matter, which isn't that problematic at 10.000 eeft up. And as it's not the finicky highly-packed digital stuff, zooming around at Mach .8 doesn't affect radio much.

Why do you say it was "radio" and "TV" instead of pre-recorded music (and pre-recorded video)?

it wasn't broadcast radio or tv on the 70s planes, but I have listened to the radio (using a small portable radio) on a plane and it's trivially easy. I live 100 miles from a transmitter I listen to at home. Adding 5 vertical miles does little. You have to change channels as you fly, but I could chase the CBC across Canada easily enough.

@KateGregory Yes but, when crossing the Atlantic... IIRC it was pre-recorded: on a loop (each channel would loop/repeat after a while), and there were no advertisements.

no argument on the transatlantic trip, but @raptortech97 expressed an opinion that altitude alone was an issue

@NateEldredge: In early 1970 they would have been CRT (the picture is LCD) and possibly black-and-white, but projector and white screen would be totally impractical. And probably even not permitted due to the very hot light bulb projectors contain.

Projector and screen were NOT impractical. About as soon as CRT projectors were cheap enough for the home, they started showing up in airplanes. The projector was mounted in the ceiling and the screen on the bulkhead. I've been on a number of widebody a/c that had that arrangement. (And they did not use a "bulb".)

@JanHudec: I don't know whether planes used 8mm or 16mm prints of movies, but either way a projector, screen, and films would weigh less than a CRT that could be viewed by all the passengers.  I would not expect a projector bulb to pose any more of a threat than any other light bulb, especially since nitrate has never used for 8mm or 16mm filmstock.

@raptortech97 Cell phone towers are deliberately made quite low power to keep their range down so they don't stomp on the next cell.  That is nowhere near the issue with broadcast radio, FM transmitters normally use enough power to push it to the horizon, AM transmitters can go farther still.  At night you can sometimes pull in AM stations from hundreds of miles away.

@supercat: When CRTs started to replace film projectors on airplanes, they were not giant CRTs, they were CRT projectors. These are tiny CRTs (3 of them -- red, green, and blue) that produce lots of light and project onto the same type of screen that film would project onto. When direct-view CRTs started to be used, it was many small ones, not a single large one.

@Gabe: Indeed, though a suitable number of small CRTs and the associated electronics would still weigh more than Super 8 film and projection equipment.  The electronics necessary to drive small CRTs have gotten smaller and lighter over the years, but I suspect the shift to video was driven more by media production cost.  Although Super 8 films were mass-produced for children's toys, I would expect that reproducing an small number of optical-soundtrack films was probably a lot more expensive [btw, I wonder why they used optical; the biggest problem I know with magnetic soundtracks...

...is that the iron oxide coating hastens the deterioration of the filmstock to which it is applied, but I don't think airlines had any concern about whether their film prints would decay after 20 years.

The picture is of fold-down LCD panels (the kind that are used today,) not the CRTs that were around back in the day.

I do not remember the small TVs till much later. It was all projected in the early days. Personally, I think they went back a step with the introduction of the smaller screens. A whole aircraft full of people laughing at that one spot in the movie is something folks no longer get to experience.

@JanHudec wrong, in the 1970s (and I've seen them even in the 1990s on older aircraft) they would use pull down movie screens and projectors. The screens would come down from the ceiling in front of the center bulkheads, projectors in the ceiling some distance behind.

There would be a number of channels of pre-recorded 'radio'-type shows, typically 5 or 6 if I recall correctly, such as current affairs, comedy, classical music, easy-listening & pop/rock, plus the movie channel or channels.
Some airlines charged a nominal rental for the headsets, while others provided them in the plastic-wrapped 'travel pack' of blanket and pillow/cushion.  Either way, they were gathered up before landing.
The earliest headsets were pneumatic, but later there were electronic ones, albeit with connectors that were pretty much exclusive to airline travel, to discourage them going astray.

The programming was on fairly short loops as well, It was funny, the music channels  had "DJs". The comedy was pretty lame. I flew in the early 70's. Looking back, it was pretty crude, but it was what we had.

I remember flying on planes in the late 70's/early 80's, where there were headphone jacks built into the armrests.  But they weren't electronic jacks; the headphones were connected by rubber tubing, and the speakers were actually in the armrest, so the sound was conducted up the rubber tubing to the earpiece.
It made the headphones extremely cheap:  they were just molded plastic and rubber tubing.

You could listen by just putting the arm rest up, max the volume and put your ear next to the plug in port. Not very comfortable at all, and both channels in one ear. They had continuous loop cassette tapes that the flight attendants started and stopped.

Three of the reasons the headphones were pneumatic were. 1) Cheap,  2) No point stealing them, 3) They could be boiled (sterilized) and re-used.

This is slightly off-topic because it is more about video than sound, however In Flight Entertainment, a Quick Look at its History says,

The popularity of in-flight entertainment didn’t really take off until
  1960 with the invention of a smaller, more portable film playing
  system that would play smaller 16 mm reels.  Soon after, the invention
  of the pneumatic headset would finally resolve the problem of being
  able to hear over the loud cabin noises. TWA became the first major
  airline to use the new system boosting them to become the world’s
  premiere airline to travel on.
The addition of the 8 mm cassette in 1971 made in-flight entertainment
  a more efficient process, mainly for the flight attendants who could
  simply change the film during the flight. The video cassette would
  dominate the way passengers viewed in-flight films until the invention
  of the DVD which would later become the primary source of all
  in-flight movies.
Throughout the late 1970s and into the early 1980s, the CRT based
  projectors began appearing on some wide body airliners. The CRT
  projector used electric beams of colored light that would beam films
  onto a fluorescent screen. The CRT was able to display a larger,
  clearer picture using both video cassettes and laser discs.

I wonder how long each 8mm cassette was?  I would expect super 8 sound film to run 20 feet/minute (compared with 36 feet/minute for 16mm), but the super 8 cartridges I've seen have generally been 50 feet long (which would be rather short).

This says that the Super 8 film was "spooled into proprietary cassettes that often held a whole 2-hour movie".

Some parts of the comments above in this article are incorrect. Before approximately 1978 there was an industrial Super 8 film projector that dropped down from the ceiling, much like an overhead video projector. The projector was loaded with a cartridge that contained the abbreviated cut of a major motion picture film. The film was Super 8 film and on one continuous loop. The movie film was projected on a flippable screen on a front bulkhead. When no movie was being shown it had a logo or some artwork on the flip side of the screen. No CRT or LCD until the 80's since there was no tape system small enough to fit on a plane before VHS or Beta's introduction in the late '70s. Later the airlines got special industrial video tape machines that worked with a specialized cartridge system developed for use in aircraft. Of course later came more advanced systems.

That's a great answer! Welcome to aviation.SE!

How would they sync the audio to the Super 8 film?

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text:
How much does a Hundred Dollar Hamburger actually cost?
Recently, the Technical Difficulties discussed the \$100 hamburger on their show Citation Needed.
A "\$100 hamburger" refers to the practice of flying to another airport, eating a hamburger there, and flying back again.
The hamburger is used as an "excuse" for flying — the actual reason is just getting flight time to meet minimal flight hours. Presumably, it once cost around \$100 to do this, which is a lot for just getting a burger.
The Wikipedia article mentions that a hundred dollar hamburger likely costs more than \$100 these days, due to increased fuel prices.
Is it feasible to accomplish this mission (in the United States) within a \$100 budget today (2017)?

Wait a minute - what?

Question is too broad (from Wiki) 100USD hamburger trip typically involves flying a short distance (less than two hours), eating at an airport restaurant, and flying home. 100USD originally referred to the approximate cost of renting or operating a light general aviation aircraft.

I'm open for any additional tags; I couldn't think of any.

I'm voting to close this as too broad as currently written. This could be a reasonable question if there was a standard metric (e.g.: two hours round trip in an aircraft rented at national average rates). As is, there will be huge variance depending on region, aircraft, flight duration, own aircraft vs rental, etc.

I edited the question to hopefully make it suitable for the site. I think it is an interesting question.

please consider using the non-clickbait title, we are not desperate for views and we don't want to mislead visitors.

@Federico okay, I won't revert it if someone changes it again (haven't got time atm to change it myself).

I thought the title quite good, yes it's slightly clickbait but it's also representative of the actual question so it's not exactly misleading IMHO. Also I didn't realise this was something pilots did and I thought it was interesting, stop being so miserable and let's allow some light hearted questions once in a while please!

When I was a kid we had a family friend who said multiple times that he was going to take me for the $100 hamburger.  He never did, but I eventually got my own license and took myself.  Haven't heard of this since then.  Also you can now actually buy said hamburger in most major metros without getting in a plane at all.

I'm so British. We call this the "Hundred and fifty quid cup o' tea"

The flight school I fly out of rents a 152 at 86USD an hour wet. Assuming you need some cash for the burger lets say you save the remaining 14 dollars for that you are right at your 100. With the 152 cruising at just about 95 Kts you need to keep the distance (both ways) under 95nm to say in our budget.
KDYL → Sky Manner (N40) is a 15nm hop and Sky Manner has a nice little restaurant.
If you want to put some actual time on the plane
KDYL → KRDG is a 39nm hop and there is a restaurant there.
Both of these hops keeps the hobbs at under or right at an hour of flying which keeps you under your total of 100USD for the flight and the burger.
That being said, there are bigger, faster, more expensive planes you can fly much farther to get food. I was chatting with a guy who flew his PC-12 from PA to Martha's Vineyard for lunch with some clients... I assume that was far more than 100$.

I have flown from my home airport to Marthas Vineyard for lunch also. My plane burns 10 gal/hour, it's about 45 minutes to get there (76 miles), so at $4.59/gallon that works out to 45/60 X 10 X 4.59 dollars/gallon = 34.43 dollars each way for gas, 68.85 total. Can even take the wife & son if we don't get too carried away with a meal.  Drive, ferry, taxi, and taxi, ferry, drive to get there & back would be an all day trip.  We did Nantucket once last year also (another 26 miles), was before Memorial Day tho so places hadn't really opened for the season.  Had a Nantucket Nectar, in Nantucket :)

It depends on location. The prevailing rental rates at a busy airport near me are around \$200/hr wet Hobbs for a C172. Only \$100 gives you about enough time to start up the plane, taxi out, wait in line, do your run-up, taxi back to the hangar, and grab a burger on your drive home. At the nearby (but less busy) field where I fly from, it's only \$150/hr and no line, so you might actually get a few laps around the pattern before running out of money.
With avgas prices of \$4-5/gal and typical light planes burning 8-10gal/hr, two or three hours of flying can easily reach \$100 in fuel costs alone. Add the cost of the plane itself—and of the burger, of course—and that burger costs a lot more than it used to.

It seems that /$ is necessary to keep MathJax from hijacking your $ signs and making unreadable text.

@FreeMan -- thanks for pointing that out, helped w/ my answer --

A "\$100 hamburger" refers to the practice of flying to another
airport, eating a hamburger there, and flying back again.
Is it feasible to accomplish this mission (in the United States)
within a \$100 budget today (2017)?

Seeing as you've set no minimum distance that must be flown, the answer is unambiguously "yes".
For example, they sell hamburgers at the airport in Salem Oregon, and the airport at Independence Oregon is only about 10 miles away.
Actually they sell hamburgers at the airport in Independence too, so you could make the trip either way.
You could even make the trip in an ultralight if you wish-- which b.t.w. the FAA does consider to be "aircraft" (see related ASE questions)-- and some are known to be based at the Salem airport, despite the Class D airspace.
You could even make a round trip with hamburger consumption at both ends, or at all three ends.  As long as future medical bills are not included in the accounting, you might still stay under budget.
You could probably even swing a round trip (including consumption of a single hamburger) in a rented aircraft from Lebanon Oregon, where as of the time the question was originally posted, a 2-place Cessna aircraft could be rented in the ballpark of 40-50$/ hr (wet).

Happy to have preemptively helped with the anti-MathJax hijacking. ;)

But does the flight have to be made in a rented aircraft?  E.g. my Cherokee burns 8-10 gph, and has an autogas STC, so I could do about 3 hours of flying and still have enough for a fairly cheap burger.  (FWIW, I don't think I've ever flown anywhere just to get a burger: I might hike, bike, or visit local tourist attractions.)

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text:
What energy density is required for the batteries in order to make an all-electric analogue of the Cessna 150 or similar plane?
I think I have some general understanding that at the present moment even with the best possible batteries, a 2 seater training aircraft (like the C-150) would be very impractical. I'm not even talking about electric analogs of the Piper Seneca, let alone airliners. At the same time, compared to piston engines, electric engines are less heavy for their output and far more efficient (I think around 90+ %). Pipistrel claims that Siemens has a 85kW engine which is only 14 kg. I also like the idea that electric engines offer us some flexibility in the energy distribution.
What sort of progress do we need in terms of energy density of current batteries, to make a 2-4 seater aircraft real and equivalent in terms of range and performance to its piston analogues? Also, will it be cheaper to charge as opposed to the cost of liquid fuel? (Assuming the electric engine is similar to a piston one in terms of power.)

Welcome to SE! Please take the [Tour] to learn your way around, as you do you'll find we're a bit different - this is a place for questions that have answers, not general discussions and opinions as you'll find at many other places. Please also stop by [Help] to see what kind of questions are on- and off-topic. This will likely be closed shortly as opinion based. If you have a specific question, we'll be more than happy to answer that, though.

Also, this question has some details about energy densities of jet fuel vs current battery technology, to address the "not opinion" portion of your question.

Cheaper to charge than what? Do you mean cheaper to run as opposed to liquid fuels?

Yes, liquid fuel. I have edited my initial post.

What do you consider to be "practical"? Some companies like Pipistrel are working on electric trainers with an endurance of 60-90 minutes because that's enough for a training session in the local pattern. That might or might not be practical, depending on how you want to use an aircraft.

Drones are by-definition light aircraft and I'd say electric drones are extremely practical already for its purpose. If you want to limit your question to manned aircraft for transportation then you should limit your question to that. But for recreation and air shows 30 minutes of battery life would make some practical use case already.

"Practical" is something of a stretch goal, but Solar Impulse have already flown a 2-seater round the world on batteries and solar power.

I agree, practical is a vague term. What I mean by practical is a full electric aircraft, capable of cross country flying, ideally with endurance which is similar to it's piston analogs. For example - 300 NM cross country flight for the CPL training.

I suggest you edit the question @ParadigmPilot, just say "equivalent range and performance"

Maybe edit the title too, since I looked at the title and immediately thought of electric VTOL taxis, which is not what you're asking about: https://www.wired.com/2017/04/uber-really-seriously-promises-flying-cars-2020/

I also see from comments on the answer that you have already given a lot of thought to this question. Those thoughts would be good to include in the question texf itself.

Obligatory xkcd cartoon: https://what-if.xkcd.com/30/

Short Answer
Batteries would need to be somewhere around 16.7MJ/kg to give the same range and performance as liquid fuels, this is about 18.5 times the capacity of the best lithium-ion batteries. Price-wise it will cost about 30-35% to charge your airplane as opposed to fill it with liquid fuels at today's prices.
Long Answer
This is a good question which is hard to give an exact answer to, so this will be more of a Fermi Approximation. To answer this you need to look at the energy contained in the fuel and the efficiency of the engine used.
Looking at the energy of the fuel I will use Specific Energy, which is the energy stored in a material per unit of mass. Specific Energy is related to Energy Density, which is the amount of energy contained per unit of volume. Often the terms are interchanged.
The specific energy of avgas and jet fuel is about 43 MJ/kg. The best lithium-ion batteries top out at about 0.9 MJ/kg (the batteries in a Tesla are about 0.7 MJ/kg), so they have a fraction of the storage of liquid fuels. The best battery technology in theoretical development (Lithium-air) has a theoretical maximum of 41 MJ/kg, more realistically they'll get 1/4 to 1/3 of that from the technology, which is still vast.
Internal combustion engines are about 35% efficient, the other 65% is wasted whereas electric engines are much closer to 90% efficient or more.
There are other factors to consider:

Weight: fuel tanks, piping and pumps take weight, and electric motors are much lighter than internal combustion engines. The batteries would need a storage structure but an electric system would probably be lighter overall
Battery inconsistencies: avgas supplies a consistent amount of energy in every single drop whereas batteries will sag as they discharge (this is regulated to give consistent power to the motor, however at some point levels will drop below what is regulatable, so not all the power in the batteries will be usable). Also, over time they lose capacity and become less efficient. Both these factors mean that you'd want to build in extra battery capacity to compensate

So I'm going to assume these two will compensate for each other, the weight savings from going electric will be offset by the need for extra capacity to ensure consistency. Assuming that all other factors are equal (propeller efficiency, etc) we can extrapolate the actual efficiency of the systems to get an approximate figure of an internal combustion on avgas: 35% of 43 MJ/kg = 15 MJ/kg of actual benefit. We can use that figure to determine what specific energy we would need from batteries to get the same amount by dividing by electric motor efficiency: 15 MJ/kg / 0.9 we get 16.7 MJ/kg.
So batteries would need to store 16.7 MJ/kg to give us the same energy as liquid fuels, but how does it compare to existing battery tech? Right now commercially available battery technology is about 0.9 MJ/kg, so it would need 18.56 times more storage capacity (16.7 / 0.9 = 18.56) to supply the same amount of energy.
As for energy costs this is going to vary a lot depending on fuel and electricity prices over time and place; we can use some of the same figures above to work the numbers. I'll assume an airplane that holds 40 US Gallons (150 liters) as the math is easy and it's about the capacity of a Cessna 172. I'm going to do separate calculations for the US and UK to see how they compare:

In the US: Avgas is about \$5.20 per US gallon at the moment, that's \$208 to fill up your airplane of 40 gals. Avgas has about 34.2 MJ/liter of energy, multiply that by 150 liters for 5130 MJ of energy. Internal combustion engines are 35% efficient and electric engines 90%, so we can calculate that an electric airplane would need 5130 * 0.35 / 0.9 =  1995 MJ of electrical power to fill up. 1995 MJ is about 554 kWh, at somewhere around \$0.135 per kWh it would cost you \$75 to charge an airplane with the same amount of energy.
In the UK: Avgas in the UK is about \$2.23 per liter (\$8.47 per US Gallon (ouch!)), so it would cost \$334.50 to fill up an airplane. 554 kWh of electricity costs about \$0.17 per kWh, so it would cost \$94 to charge the airplane

EDIT:
I did consider the efficiency gain from weight loss as fuel is burned, i.e. a variable mass system, I left it out of the answer as it isn't significant compared to the other factors in what is already an approximation. It has to do with the fuel fraction, which is the percentage of the aircraft weight that is fuel, which on a light piston single is comparatively low. A Cessna 172 carries about 40 gallons of fuel, 38 of which is usable, weighing about 228 pounds as opposed to a typical take-off weight of 2200-2300 lbs. In other words its fuel fraction is about 10%, even on a long range flight using every bit of fuel you will only lose 10% of your weight, and I would approximate that you'd get around 5% benefit from it. This was not enough of a factor compared to the other considerations, and it would probably be offset by regenerative descents where the electric motor actually generates power from the spinning prop.
For airplanes where a more significant portion of the weight is fuel, i.e. a higher fuel fraction, efficiency gains from variable mass is a much more significant factor, for example an A380's fuel fraction is 44%.

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An all-electric craft similar to what you described has actually been created (IEEE Spectrum did a nice article about it).  The batteries are described as 260 Watt-hours per kilogram with a power plant output ratio of over 5 kW/kg.  The two-seat craft is designed for training flights, and the fuel for each hour of flight time costs less than one-eighth the cost of a conventional-fueled aircraft.  The aircraft's official specs indicate that the 2-seater version has about 3 hours of flight time (4 hours for the 4-seater).  It uses the same sort of "supercharging" outlets that electric cars use, but there's no specific numbers regarding recharge time.
The article discusses the technical development of the craft and many of the scaling issues that you mentioned; some were able to be engineered around, but some (including battery storage density) remain a problem for the foreseeable future.  To summarize, electric drive is currently competitive only in slower aircraft.  Drag increases with the square of speed, more drag means more batteries needed to supply the power, and that means more weight.  Battery energy density ultimately limits the size and speed of an all-electric plane, but current technology appears to be plenty sufficient to produce a practical aircraft.

Good article. However, they don't give any flight endurance numbers. And this is what in my opinion one of the key points. I assume their aircraft would be similar to Pipistrel in this regard - 1 hour with reserves. It's about 5 times less then similar pistone engine aircrafts.

@ParadigmPilot Updated with additional details.  Flight time is in the 3-4 hour range depending on model.  These were designed as training craft so long flights weren't an explicit design goal.  The article alludes that a hybrid design (electric drive, plus small gas engine to recharge batteries) is likely to be the future for larger craft or longer flights.

I like their design, but it's really hard to believe that the 4 seat Sun Flyer (with 130 kW engine) is capable of 4 hours flight. If it's true, then it somewhat contradicts the approximate power density figure of 16.7 MJ/kg given in the 1st  answer. If it's capable to achieve 4 hours with the current technology of 0.9 MJ/kg then even 3-4 MJ/kg of power density could make any piston aircraft of similar capacity potentially obsolete.

A key assumption in GdD's answer is that things like propeller efficiency stayed the same, which isn't the case for the Sun Flyer.  The small motor means a slimmer cowling, which they claim reduces air resistance by 15% and allows the prop to generate "considerably more thrust".  Electric-specific optimizations like this (and regenerative braking) reduce the necessary power density, and you'll likely see more and more of these as time goes on.

It's a very good point regarding the propeller and cowling efficiency of the Sun Flyer. But let's have a look at Cirrus SR 22 or Diamond DA 40. They both use composite materials and likely have better aerodynamics than Cessna 172. The cowling area of both Cirrus and Diamond looks more streamlined compared to 172, but I totally agree though - the Sun Flyer, with no cowling air intakes, is likely aerodynamically better.

Continue with my previous comment: clearly, we need more real life numbers, especially the range figure of the Sun Flyer is really important. Meanwhile, the 4 seater Cirrus SR 22 is capable of 1900 km range, while carrying it's parachute system - an unattainable figure for similar capacity all-alectric aircraft.

You're missing the point. Electric vehicles don't even try to match energy density of petroleum.
This isn't a matter of yank out a Lycoming and drop in a VFD and induction motor and battery bank. Even electric cars take a blank-slate approach.  They don't simply mimic the ratio of powertrain mass to rest-of-vehicle mass.  They design a new vehicle that is workable.  You bet you'd do the same thing on an airplane.
Keep in mind an electric motor is much smaller and lighter than an aircraft engine, and power can be distributed around the aircraft, e.g. a multi-motor electric plane is perfectly reasonable and almost inevitable.  Whereas a multi-engine gas plane is a wildly different creature with very different certification.
That means your props are in better places, making more of their swept area, instead of stuck in front of bulky engines or otherwise wasting energy trying to bend air around a fuselage. They could blow the wing, or be centerline thrust using 2 motors per contra-rotating prop.  You want more rudder authority at low speed? Blow the rudder. You can put 'em anywhere.
Also a factor is that aircraft have nice large flat surfaces that lend themselves to solar panels.  This adds mass but also adds range in day-flight, which then raises the question whether this is a day-only or night aircraft.  All that calculus has to go into vehicle design.
Another part of the calculus is lightweight materials like composites.  It doesn't make sense to use Dreamliner or F-22 construction methods on a cheap basic GA aircraft, but when it is critical to range/performance, you revisit that.  And it could become affordable in mass production.
You bet energy density helps but it may be possible to build a usable aircraft with existing tech.  You just don't know until you iterate on vehicle design and see where it goes. That's not cheap.

Solar panels are a bad fit for aircraft. Even with impossible perfect solar panels,  the sun's output is just too low for it to make a meaningful difference.

@Antzi:  Solar Impulse http://www.solarimpulse.com/ and Solar Stratos https://www.solarstratos.com/en/ have both put on good showings for solar electric planes.  Exotic, for sure, but it's incorrect to count them out entirely on aircraft.

@ErinAnne correct, but this will sadly remain the domain of exotic planes; quite unlike OP's Cessna

@Harper I'm only talking about in flight solar power, not electric airplanes in general.

@Antzi oh, okay.

@Harper I agree with what you say. Majority of your points were already mentioned in the answers and comments. There's definitely no need to mimic the power density of the fuel, hence the very approximate number given in the first answer is 16.7 MJ/kg and not 43 MJ/kg. Also, read my comment to the second answer regarding Sun Flyer aircraft.

I'm with you here.  To start, take a design that's more like a motor glider than a trainer.  Then optimize every part around the electric power system.  It doesn't need to consume as much power, for as long, as a C152 -- it just needs to be able to stay aloft at a similar cruise speed for a similar time.

Here's a rule of thumb: you can assume that the range of a practical electric aircraft, in nautical miles, is approximately equal to the energy density of its batteries, in Wh/kg. Today, that number is about 250, tops.
That rule of thumb assumes that the cruise L/D is 20:1. If your design gets 10:1, halve the range.
Is 20:1 realistic? Well, a Cirrus SR22, a modern all-composite airplane, gets about 17 at a best L/D around 90 kt. So, 20:1 is ambitious, but realistic.
If your idea of "practical" is a 160 kt cruise speed, you'll need an airframe with an L/D of 20:1 at 160 kt, that also has a big enough wing to slow down to 60 kt as required by Part 23. That's hard. Or, you can get 10:1 at 160 kt, meet Part 23 requirements, but halve the range.
If your idea of "practical" is a range of 600 NM, you'll need batteries with 600 Wh/kg. They don't exist.
If 90 kt cruise for 250 NM is your idea of "practical", the technology is good enough today. And, 120 kt cruise for 250 NM may be feasible with clever airframe design.
Let's turn to the system engineering behind this answer.
Energy required = Force x Distance = Drag x Range = [Weight / (L/D)] x Range = Energy stored in the batteries
$E_{req}= F \cdot x = D \cdot R = \frac {W\cdot D}{L}\cdot R = E_{bat}$
With:

$E_{req}$ = energy required
$F$ = force
$x$ = displacement
$D$ = aerodynamic drag
$R$ = range
$W$ = weight
$L$ = lift
$E_{bat}$ = energy from the battery

So,
$R \approx \frac{ E_{bat}}{W}\cdot \frac{L}{D}$
Weight = Payload + Electric power system weight + structural weight
For a practical aircraft, the structural weight is approximately half of the total weight, maybe a little less. Let's call it 0.5 if we include the weight of the electric motor, which will scale with the aircraft weight.
So, if the structure including the motor is half the total weight, we have
$W \approx 2 (W_{payload} + W_{bat})$
Let's define $k$ as the fraction of the lifted weight (i.e., Payload + Battery) that is battery.
So, $k = \frac{W_{bat}}{W_{payload}+W_{bat}}$, and therefore $W_{payload} + W_{bat} = \frac{W_{bat}}{k}$.
So,
$W \approx \frac{2 \cdot W_{bat}} { k}$
Then,
$R \approx \frac{E_{bat}}{  W_{bat} }\cdot\frac{k}{2} \cdot \frac{L}{D}  $
This needs one adjustment: the energy available from the battery in practice is not $W_{bat}$, but rather $U \cdot W_{bat}$, where $U$ has a value of about 75%. This is because if you fully charge and discharge the battery on each cycle, using the full amount of $W_{bat}$, the battery will not last for many cycles.
So, we adjust to show
$R \approx \frac{E_{bat}}{  W_{bat} }\cdot\frac{k}{2} \cdot U \cdot \frac{L}{D}  $
Now, that's all in SI units, where Distance is in meters, energy is in joules, and weight is in Newtons (not kg!). Let's do a unit conversion:
$R = 1852 \cdot R_{NM}$
$E = 3600 \cdot E_{Wh}$
$W_{bat} = 9.8 \cdot M_{bat, kg}$
So,
$1852 \cdot R_{NM} \approx \frac{3600 \cdot E_{Wh}}{ 9.8 \cdot M_{bat, kg} }\cdot\frac{k}{2} \cdot U \cdot \frac{L}{D}  $
and thus
$R_{NM} \approx \ 0.0743 \cdot \frac{E_{Wh}}{M_{bat, kg} }\cdot\ k \cdot \frac{L}{D}  $
or, if we assume $\frac{L}{D} \approx 20$
then
$R_{NM} \approx \ 1.48 \cdot\ k \cdot \frac{E_{Wh}}{M_{bat, kg} }$
The maximum possible range is if $k = 1$, i.e., there's no payload, and the aircraft carries nothing but battery.
But, for a more practical design, if we set $k = \frac{1}{1.48} = 0.67$, i.e., the battery weighs twice times as much as the payload (think of it as 200 kg of battery, or 440 lb of battery, per person carried), then
$R_{NM} \approx \frac{E_{Wh}}{M_{bat, kg} }$
Which is the rule of thumb: range in nautical miles equals energy density in Wh/kg.
More precisely,
$R_{NM} \approx \frac{E_{Wh}}{M_{bat, kg}} \cdot \frac{\frac{L}{D}}{20}$
You could add more range by having a bigger battery fraction k, but going from battery weight of 2 x payload to 4 x payload only adds 20% to range - not very exciting.
Note that the basic rule of thumb assumes quite a high $\frac{L}{D}$ ratio of 20:1 in cruise. Note also that it says nothing about speed or altitude flown: ultimately, all that matters, for range, is cruising $\frac{L}{D}$ and battery energy density.

Hello Finbar, welcome to aviation stackexchange. You might want to look into MathJax notation for the formulas. MathJax make the mathematics in answers more readable, and many people appreciate that here.

With much less cooling requirements of electric propulsion, the L/D of 20 should be easy to achieve if the aspect ratio can grow above 12 or 15. However, that will shift the best range c$_L$ further up, so flying far needs more patience. However, if I enter the numbers before your unit conversion, I get about twice your range: 200 Wh/kg, k=2/3 and L/D=20 comes out to 489 km.

@PeterKämpf, You're right, the lower cooling requirements are a big help, which is why I think 20:1 is quite reasonable if you're not in a hurry to go places. Indeed, 40:1 - or more - is quite achievable if you can accept an aircraft with the wingspan and handling characteristics of a sailplane (an electric Stemme S10 might have a significant range, but risks being called "impractical"). But, 489km is 264 nautical miles... You're right, I rounded quite a bit. But, don't forget you can only access about 80% of a battery's rated capacity, which I omitted too.

@PeterKämpf, thanks you your comment I realized I used 2600 instead of 3600 in the calculation. 60 x 60 = 3600, not 2600 (ouch). Fixed that. Added the battery usable fraction of 75%. All of which brings us back to the original answer (which I knew) but with better engineering (which I was reconstructing from memory). Thanks for that!

This plane is comparable to a C150, altho less baggage area if you wanted to take a short trip.  We upgraded from a C150 to a C177B when baggage area (and a child going on 2 years old) became a driving factor. Had even purchased some cable and turnbuckles to try and find a way to secure a car seat (which ended up in the basement, never used, as the C177 was purchased pretty quickly (lucky timing on the GA marketplace)).
https://www.pipistrel-usa.com/alpha-electro/
I don't see if they talk about battery energy density tho, might have to download one of the information booklets to find that.

High capacity, easy to replace dry-type 12V battery
aircraft fitted with 60 kW electric motor.
nominal battery capacity 21 kWh
engine 50 + kW @ 2100-2400 rpm
standard endurance, traffic patterns 60 min + reserve
standard range at cruise 80 kts 70 NM (130 km)
Standard Battery System
Maximum voltage 399 V
Minimum voltage 297 V
Recommended voltage range for storage 345 V - 365 V
How long does it typically take to charge the batteries with the
  different chargers? (20%-95% range)
6hrs with 3kW charger, 1h 40' with 10 kW charger, 1h 5' with 14 kW, 45
  minutes with the 20 kW charger
How heavy are the batteries and can I swap them over myself?
  Each battery pack is 53 kg. Yes, you can remove the pack with no extra help
What kind of batteries are installed?
  Lithium ion. Cells are manufacturer by Samsung. Battery box design and
  assembly is Pipistrel, Battery Management System (BMS) is also designed and
  manufactured by Pipistrel

Enough info there to do the math?

It all depends upon what range or performance profiles you would like out of the airplane.  Electric aircraft - or at least prototype electric aircraft - which have similar performance in terms of speed, useful load, etc to petroleum powered analogs.  It’s just that the energy densities of the batteries do not allow for a useful endurance.  Current designs like Pipistrel’s Alpha Electro have about a 1 hour endurance plus a day VFR reserve of 30 minutes of power in an economy cruise.  When compared to an analogous Rotax powered LSA with over 6 hours of endurance plus reserves, you quickly see how limited this is.
It would be better to ask as to what energy density would be needed to match the performance and endurance of existing petrol powered light aircraft while matching their useful load.  As mentioned above a density of approx 15 MJ/kg would allow for this.  This will require a considerable leap in electrochemistry technology to store and deliver that kind of energy reliably and safely.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What level of damage to an aircraft is acceptable to let it depart?
Yesterday (28 June 2016), a Bombardier Q400 from EPGD to EPWA made an emergency landing because of a blown tire, spotted by a passenger. Everything went smoothly and the plane landed successfully assisted by fire trucks.
You can see the article and video here (in Polish).
In addition to the damaged tire, I've spotted that there is some damage to some parts of the plane:

Is it okay to fly with that?
I guess it isn't important for the safety of the flight (it looks like some landing gear cover or something), but what damage to the airplane is considered safe for flight?
Is it possible to force the airline to repair non-critical parts?
I know that loose parts of airplanes could do harm when they fall off, e.g. during takeoff, and stay on the runway (like in the Air France Flight 4590 Concorde crash).

Hello Mark, welcome to Aviation.SE!

This doesn't answer your question, but to me it seems that the damage to the gear cover was likely caused by the blown tyre.

I think rules a very strict in general. A notable exemption is a ferry-flight, it is okay to take-off with only three initial running engines on a four-engine aircraft. With passengers on board probably no one will take-off, but proceeding to desination is maybe possible (but fuel/drag need to be considered). Examples are (as always Terry) a B747 http://aviation.stackexchange.com/q/16515/1084 or A380 http://www.avweb.com/avwebflash/news/A380-Flies-5000-Miles-On-Three-Engines-220951-1.html

"Is it possible to force the airline to repair non-critical parts?": Any aircraft got parts that are not working (e.g. a thrust reverser). It would cost a lot and wouldn't help safety significantly to have all parts in perfect conditions (the passenger wouldn't understand paying twice the price for something that is very unlikely to cause a problem). To sort between nice to have and mandatory equipment, there is a list of devices that must work before dispatching the flight: The Minimum Equipment List, MEL.

Nice list, thank you. But there are mainly cockpit indicators and accessories that are mentioned there. What about external parts, like that landing gear cover? Is it mandatory to have it?

Gears are covered starting page 97 (32-1) of the MEL. MEL is complemented by the Configuration Deviation List (CDL) which lists which parts may be missing and the Aircraft Maintenance Manual (AMM) which describes the degree of damage allowed to the airframe. I cannot find related examples online. Hopefully, someone in the real business may provide additional information.

Aircraft Maintenance Engineer here.
To evaluate if an aircraft is safe to fly we use three main reference documents:
1. MEL (minimum equipment list).
This document contains the list of elements that are allowed to be inoperative.
For example a pneumatic valve, a computer, a seat, etc...
All unserviceable elements will have to be fixed within a predetermined duration/limit.
(Usually 1, 3, 10 or 120 days)
If the failure is not fixed by the due date, the whole aircraft will not be released to fly. (No matter how small the fault is)
2. CDL (components deviation list).
This document contains the list of components that may be removed from the aircraft.
For example a damaged refueling service door can be removed, if the maintenance team is unable to fix it before departure.
These will usually be associated with performance penalties.
CDL defects will also come with a deadline.
3. SRM (structural repair manual).
This manual contains all information needed to evaluate structural damage such as dents, scratch, lightning strike.
This manual will also give you the information needed to evaluate if a damage is "no-go" (meaning the aircraft is not safe for flight) or if the damage is within tolerance.
If it is within tolerance you will also get time or aircraft cycles limitations (a cycle is a takeoff and landing)
Regarding your picture:
The plane will not be allowed to fly with a blown tyre. A blown/damaged/worn out tyre is a no-go.
However, airliners are designed to land safely with one blown tyre. Aircraft incorporate lots of redundancy so as to eliminate single points of failure — for example, most commercial jetliners are designed to be able to land safely even if they lose an engine. Efficiency, comfort, and ease of operation may be reduced but the situation can be kept under control and is still within the aircraft's design specifications.
I can see damage on the landing gear door. It is possible that an aircraft would be allowed to fly with the landing gear door removed if a fix cannot be performed before departure, however; the aircraft may experience increased drag. This would be covered in the CDL.
The aircraft should also receive extensive inspection before departure and after landing.

Technically, an airliner can land just fine with all engines unserviceable, as long as it can make it to the runway. :) Climbing out with all engines unserviceable is more of a problem, though. In all seriousness, though, good answer.

Just to add that engine manufacturers - and I assume aircraft manufacturers also - provide a 24/7/365 "technical hotline" service to give professional advice about situations which are not explicitly covered by the documentation and regulations. These days, there is no big problem setting up a live video link between a maintenance engineer on the ground operating a camera, and a technical specialist on the other side of the world. (Some of the in-service issues that arise are truly surreal - but that would be going off topic!)

So you mean if a seat doesn't recline in coach, and they don't fix it in (let's say) 120 days, the whole plane is grounded? That is harsh!

@corsiKa -- yes -- the idea is that the plane will be overnight-or-longer at a main hub/maintenance base and/or receiving a light check (such as an A-check) before that 120day interval is up, giving the mechanics time to fix the busted seat or what-have-you.

@alephzero -- They do indeed; the major airframers can even send out an emergency repair crew if needed (aka their AOG team) -- this would be needed if something really bad happens at an outstation like getting your tailfeathers spindled on a fence post.

@corsiKa that's correct but very unlikely. A seat is usually a quick fix and create lots of trouble is left unserviceable to long (loss of revenue mainly)

"MEL ... contains the list of elements that are allowed to be inoperative." Surely you mean those that are not allowed to be inoperative (or alternatively, those which are required to be functional)? Otherwise it wouldn't be much of a minimum equipment list, would it?

You might want to add that no gear leg in todays airliners has less than two wheels purely for redundancy. And yes, the airplane could operate with one of them inoperable, but for far fewer hours and with weight restrictions, so in certain circumstances (fly back empty to repair base) the plane is good to fly with one wheel less.

@MichaelKjörling Actually the MEL is both what the OP said and what you think. As the OP said the MEL does not list all components of the aircraft, only ones that can be in an inoperative state,  so if a component is not on the list, then it must be operative.. But, as you said, for the ones that are on the list, it indicates the minimum number of components that are required to be operative. For instance if there are 5 alternators on the aircraft, it may say you can dispatch with only 4 operative... or something like that.

I'm guessing they didn't take off with a blown tire; I assume it blew during the takeoff roll. So the next question is: why return to the point of departure rather than continue to the destination (assuming both airports are equally well equipped to deal with a blown tire.)

The other answer goes over the MEL/CDL/SRM, but I'll address your specific questions:

Is it okay to fly with that?

(I assume you are talking about the gear door, not the tire) That depends, specifically in this instance I doubt that there would be any issue flying with that small amount of damage considering it is on a gear door on the bottom of the engine pod. I would, as a pilot though, want my maintenance people to look over it for damage you can't see on this side, perhaps rubber flew up into the gear bay and broke/dented a hydraulic line, etc. If it really is as superficial as it looks, it would probably be OK.

I guess it isn't important for the safety of flight (it looks like some landing gear cover or something), but what damage of airplane is considered safe for flight?

Gear doors can tear off and rip through other parts of the fuselage, like the tail, so they can be safety critical if damaged enough. As far as what damage is considered safe for flight it really depends on the damage and its location. Some damage that cannot be seen like JAL Flight 123 which had a damaged aft pressure bulkhead from a hard landing 7 years prior. Hard landings may not have any outward appearance but hide dangerous internal damage.
The only way to find out if its safe to fly is to have it inspected. Only then can it be determined if the damage would render the flight unsafe. I don't know of any pilot that would look out the window, see damage, and determine it was safe to continue. Typically after noticing damage the next thing you do is look for a place to put it down and inspect it.

Is it possible to force the airline to repair non-critical parts?

I'm not sure who you are talking about doing the forcing? If it is you as a passenger, you could simply bring it to the attention of the crew and if you don't have a satisfactory answer, re-book your flight. You could even tell other passengers you don't feel safe due to XXX. Considering how many times I've been delayed because there was an issue with the pilots seat sliders on an ERJ, I'm guessing most times the crew knows about it and maintenance is on its way. However if you notice something, speak up, it may save some lives. Just be discreet (don't scream and yell because you see dirty rivets), crews are pretty good about wanting to make it there alive and will take any concerns seriously.
If you are talking about the airline doing the repair versus the manufacturer, this happens pretty often. Most airlines have maintenance crews for that reason.

Excellent point about the crew wanting to make it home alive, too.

@FreeMan Crew is under financial pressure from the airline so technically they are the least inclined to make it home alive of all people on board (unless a suicidal passenger happens).

@Agent_L if you're more concerned with money than making it home to see your spouse, children, parents, pets, whatever, I pray to God that you're never in charge of a passenger flight. Aside from that, I don't see what the company wanting to maximize profit has to do with a pilot's desire to return to earth in one piece.

@FreeMan https://en.wikipedia.org/wiki/2010_Polish_Air_Force_Tu-154_crash Pilots pressured by their superiors into killing everyone on board (pilots, the superiors and nearly hundred of innocent bystanders).

@FreeMan It's not "I'll give you $100 more if you kill yourself". It's "Do what we tell you, or you'll have no job to support your spouse, children, parents and pets". I pray to God that you're never in charge of anything if you refuse to admit that people can be pressured into most stupid things.

@Agent_L They may be under pressure to perform which has financial consequences, but they are not any less inclined to make it home alive than the passengers they fly (especially given that flights kill a majority of the passengers in a crash). Unless they are suicidal they want to make it home alive just as much as anybody else, financial/performance pressures or not. The difference is susceptibility to perform outside of their skills or comfort, passengers are along for the ride, the pilots make the decisions.

@RonBeyer Now we're splitting hair over what really "inclined" means. I took it as "if you're doing something, it means you were inclined into it"

Another example - this time from here and not as tragic, read the last paragraph: http://aviation.stackexchange.com/a/29674/3903

Either way you want to define "inclined" (which means disposed, not pushed or persuaded), and taking a "live if land, die if crashed" (not looking at crash survivability statistics), a pilot is no more or less likely to make it home than any of the passengers on that flight. Regardless of a pilots actions, the crew wants to make it home alive, which is the original point. They may be pressured into doing something stupid, but they still want to see their families at the end of the day...


text:
Why does the A340 have 4 engines instead of 2?
I have noticed for a while the A340 has four engines and the Boeing 777 only has two engines and they are about the same size. So why can't an A340 have two engines instead of four?

A340
. B777

On a jumbo jet like the B747-8 four engines are a requirement.

Not strictly duplicates, but you might find relevant information in Why does the 747 have 4 engines instead of 2? and Does adding more engines to commercial aircraft increase safety?.

Before McDonnell Douglas being takeover by boeing, they developed a new 2-engine airliner similar to b777, and ask Airbus for fund and development. However Airbus was designing a380 and rejected the proposal.

The A340 was designed at a time when ETOPS (Extended-range Twin-engine Operational Performance Standards) had not been developed. Some airlines preferred two engines which reduced operational costs, while others preferred four engines with increased reliability at an additional cost.
Airbus decided to split the development into distinct aircraft having the same wing and airframe - A330 with two engines and A340 with four engines.
However, as time has passed, ETOPS has become the norm with improved engine reliability, and A340 production has been stopped. Almost all the civil airliners under development now have two engines.
The Boeing 777, on the other hand, was developed with twin engine operation in mind.

Very informative. I am concerned flying over the Pacific in two engine planes. Volcanic ash, etc... Even birds at 37,900 feet! (Nov 29,1975: Ruppell's griffon vulture, Ivory Coast). I guess remote monitoring of engine state works well.

This is not quite true, ETOPS predates the A330/340 by quite a bit. The issue is, when the A340 was introduced, the norm was ETOPS-120 (i.e. you had to fly routes with a diversion airfield within 120 minutes of flight time), which limits the routes you can choose. These days, ETOPS-180 is the norm and some aircraft are certified for ETOPS-240, which makes more routes available. https://en.wikipedia.org/wiki/ETOPS

@Hobbes I'd suggest editing the original post to correct that, it is indeed incorrect that ETOPS didn't exist when the A340 was being developed.

I don't mind making minor changes to someone else's post, but a change this big would change the intent, and I'm not comfortable doing that.

If it had only 2 engines, it would be an A330. The main difference between the two models is that the A340 has four engines, and it was designed and produced specifically for airlines that needed that.
At the time the A330/A340 series was designed, having more than two engines was an operational benefit because a two-engined plane needs to stay within a certain range of diversion airfields, which made the A330 unsuitable for some routes. This benefit has since become smaller due to improved reliability of engines (or improved trust in the reliability), since the maximal distance from nearest landing opportunity is determined mainly by how long time you dare to need a plane to stay aloft after an engine failure enroute, before the risk that the remaining engine will randomly fail too becomes unacceptable.
The A340s that are already built keep flying until they reach the end of their operational life, of course.
The only large quadjets still in production are the 747 and the A380. The A380 needs more than two engines because of its size, in order to produce enough takeoff thrust. The 747 might conceivably have ended up with two engines if it was designed from scratch today.

Regarding your last statement about designing the 747 as a twin jet... that's debatable, those would have to be some seriously big engines. But you could also argue that the new 777X will come pretty close in capacity.

@fooot: That's why I wrote "might conceivably" instead of "would probably".

Inconceivable!!

I have a model of an Airbus A340-600 and a Boeing 777-200 and it is easy to notice by size that the 777-200 uses more powerful engines:

(top: 777, bottom: A340)


text:
Can the two female belts in Jurassic Park be anything else but a wrongly installed belt?
In Jurassic Park, when the party arrives on Isla Nublar, Dr. Alan Grant discovers his seat belt has two female ends. He makes it work, foreshadowing that in nature as well, a population of only females can "make it work" — the dinosaurs are breeding!

How on earth can a seat with two female belts have ever passed inspection?
Or is there something else going on? I'm not familiar with the model of helicopter, but can there have been a mistake, where the people in the seats next to him — John Hammond and Dr. Ellie Sattler — took the wrong belt, leaving him with a female end where he should've had a male end?
Labeling the seats from A to D, with Dr. Grant in seat A, Dr. Sattler in seat B, and Hammond in C, and belts labeled F and M, is the following configuration possible in this model helicopter?
AF|Grant|BF|AM|Sattler|CF|BM|Hammond|DF|CM|empty|DM

That means the helicopter needs to have four seats in a row. Does this model have four seats in a row?
Or did Dr. Grant leave someone else with two male ends?
Is there another solution that explains why he failed to locate the correct belt? Or is there no excuse and should an anonymous mechanic have gotten a citation?

Basically, my question boils down to:
Does this model helicopter have a configuration with four seats in a row?
If not, is there any other explanation other than a wrongly installed belt?

He simply grabbed two of the wrong ends. Someone else is probably sitting on the other half.

"How on earth can a seat with two female belts have ever passed inspection?" I'm not an expert, but this was probably in the screenplay and no one was faulty.

It was an element of a Hollywood screenplay used for light comedy and to cement the idea of Sam Neil's character being mechanically inept but practical with the audience.

Sounds like a typical Hollywood trope

He has simply picked up  the end in his right hand which belongs to the belt of the person sitting on his right.
If you have two people sitting side by side with lap belts then there will be two belts in between them eg
F-(passengerA)-M-F-(passengerB)-M
As mentioned in the comments there is a good chance that he is siting on his own male-ended belt.

That's my suggestion, but that would need the helicopter to have 4 seats in a row. Does that model have that?

@SQB Why 4 in a row? The answer clearly shows it can happen with 2 and you can see in the video there is 3.

@Notts90 because the other two people are seated and belted correctly, which means there must be at least 4 female seat belt ends. So either at least 4 seats, or an FAA violation.

You don't actually see  that the other two people in the row do have their belts done up. In fact it looks like Sattler  can't find hers either (0:46)  then sees that  Grant has got two female buckles and realises what has happened. Hammond actually leans over to try to sort it out (1:05) which suggest that he hasn't got his on either ie Grant takes the wrong belt before Sattler has a chance to.

@SQB basically what Chris said above.

Of course since there is nowhere to walk in a helicopter, they should have been buckled up since before take-off and not hurriedly buckling up just before landing.

At 1:05 there is no seatbelt visible across Sattler's lap. Grant grabbed her end and his, making both belts unusable.

@ChrisJohns if you add your comment about the others in his row not being able to find their belts because Grant took the wrong belts to your answer, I'll accept it. I don't feel comfortable editing it in myself.


text:
Why is tape being applied to this jet engine?
When I read this question asking for identification of the aircraft, my immediate question was:
What is that duck tape for?
Whether you call it duck tape or duct tape, why is it being applied to the nacelle?

It's being applied to keep the nacelle from falling off, of course.

@PeteBecker close, but no cigar; the nacelle is usually held on by crazy glue. The tape is speed tape, which makes the plane go faster.

It's not duct tape. It's speed tape.

Speed tape is an aluminum pressure-sensitive tape used to do minor repairs on aircraft and racing cars. It is used as a temporary repair material until a more permanent repair can be carried out.

Probably just got a bit of a gap around the cowling or perhaps a loose fastener or two. It's common practice for sealing minor gaps and things until it's next in the hangar for work.
Whilst I was Googling for speed tape, I also found these:
http://www.askthepilot.com/duct-tape/
This is how the wonderful British "tabloid" press deal with aviation stories.  Top marks for getting the "shocked passenger" phrase in.

Wow - at first pass, I thought the Speed Tape was much like the Speed Holes in Homer's car.  Thanks for the answer and details!

To be fair, if I, as a passenger, saw a worker apparently duct-taping the engine on a plane I was about to hang around up in the sky in, I’d probably be reasonably shocked as well. And to give them their fair dues, they did spend most of the article explaining how it’s not duct tape but actually perfectly normal and absolutely up to safety standards.

Other than the price tag, and the fact it takes some brute force to get off the roll, I'm sure you'd probably want to trade your duck tape in for a roll of speed tape ;)

@JanusBahsJacquet: I find  assuming that maintenance personnel don't know what they are doing more shocking than the opposite.

@MartinArgerami Being shocked at seeing something very unexpected doesn't equal assuming it is wrong. If I looked out the window and saw someone putting (what looks like) duct tape on a nacelle like that, I would have been shocked and thought, “Is that for real? WTF?!”. I wouldn't assume maintenance didn't know what they were doing, but it would shock me that taping up an airplane was apparently something to be done. And I'd be quite likely to take a picture and tweet about it, too.

@JanusBahsJacquet: You may take one minute to include in your reasoning, before being "shocked", that an airline that owns or leases a $100 million to $300 million aircraft is not in a hurry to not take care of it. In the past, when we didn't know, we assumed things were handled correctly by those who know, it seems that today, everyone wants to challenge skilled professionals, even in a domain which is one of the most regulated and safe ones.

@mins My point is that shock generally comes before reasoning. Once you've reasoned, there is no possibility of shock.

@BruceWayne It probably happened just like that scene from The Simpsons too. Someone was applying duct tape to the plane and someone said "Hey! are you fixing the plane with duct tape?" "No, this is speed tape, it makes the plane go faster"

@KodosJohnson and you know they were waiting for someone to ask just that question. Hahaha, apropos username too!

If I looked out the window and saw that, before reading this, I probably would have gotten off the plane, just to be fair. With big commercial airlines cutting costs by making passengers share a can of soda, I could totally see them "saving money" by "speed tapping" something that really should have been taken into a hanger and fixed.

@JanusBahsJacquet "My point is that shock generally comes before reasoning". Maybe for certain types of people it does, especially these days. Definitely not "generally", though.

This doesn't answer the question at all: why? Whatever that tape that is, OP is asking why are they putting it there. "To repair the airplane" seems to obvious to be helpful.

I've heard the US Army used speed tape to protect the edges of helicopter rotor blades against the effect of sand against the blades in Iraq during Operation Desert Storm.

Being obvious doesn't make it wrong or unhelpful. @user3528438

Why include a link to the mirror? You are driving traffic to a terrible, unethical website. Please remove that from the answer.

@coteyr really? you could totally see that because they want to save money on mixers by suggesting that couples share a can (which seems fairly logical, especially if they notice they often throw away half-finished cans of mixer), they also want to gamble the loss of a $xxx million aircraft? i'm sorry, but walking off the aircraft because you see a highly-trained maintenance worker carrying out a procedure you know nothing about is a little crazy.

At least on the flights I have been on they don't ask couples to share. They split a can of Sprite between three strangers and then expect you to pay if you want more. And yes, I assume that if a company is that cheap they look for any way to save money. Like https://en.wikipedia.org/wiki/American_Airlines_Flight_191

@coteyr You're being paranoid and forgetting that the FAA regulates aircraft maintenance in the USA, and there are other regulation bodies throughout the world. But they don't regulate splitting a can of soda. You're making a false equivalence. Speed tape on a cowling is not an unreasonable maintenance procedure and is a regulated form of maintenance. Don't spread FUD.

@mins I go by "trust, but verify" which is how I meant my question. I don't assume that guy is MacGyvering it, but it is a somewhat unusual sight, hence my question.

SQB: Curiosity is certainly a quality and I upvoted your question. My comment was only aimed to "To be fair, if I [...] saw a worker apparently duct-taping the engine[...], I’d probably be reasonably shocked as well".

@JasonC Yes, absolutely generally. Shock is an immediate reaction that happens  with no reflection; reasoning is not. When you hear a balloon pop, the shock makes you jump before the rational reasoning that it’s completely harmless hits you. The same is true when you see something that appears bizarre to you. If it did not register as shocking or surprising, there would be no need to reason about it at all.


text:
Was ATC overstepping its boundaries when advising a pilot to ignore a cell warning?
I found a clip on YouTube (via an article on Jalopnik) of an Aer Lingus pilot departing from JFK. Due to a weather cell showing up on his instruments, he can not make the left ATC asks him to make.
ATC advises him that the weather is not as bad as the pilot makes it out to be.

ATC: "Shamrock 104 heavy, it's light. I have 6 categories of weather here, it's the lightest category. I've had no adverse ride reports south of the airport by 10 miles."

He then is put in a holding pattern (while departing) until the situation is resolved. He is then told that the last 6 craft departing had no problem following that heading.

ATC: "Shamrock 104 heavy, you're gonna go the way the last 6 GREKIs went while you did this overhead Kennedy."

Was ATC overstepping its boundaries advising a pilot to ignore a weather warning?

Related

The controller didn't overstep his boundaries, and he didn't tell the pilot to ignore a weather warning.
Shamrock demanded something that's extreme for the NYC airspace: runway heading for 15 miles. Usually asking for right or left deviation is sufficient, and that appears to be what the previous Delta departure did.
Once Shamrock declined an easterly heading, the controller had no choice but to vector them in a temporary hold. The controller was frustrated because the previous departures had been accepting turns to the east and his radar didn't show signs of significant precipitation. He also astutely pointed out that this weather was 5 miles from the runway departure end. Aer Lingus should have been able to paint that on their radar or see it with their eyes before they departed. Their clearance was to the GREKI fix so they knew they'd be heading that way after departure. That doesn't mean Shamrock was wrong. After all, they are flying in actual, and the controller is sitting in a room at zero knots, but in the incredibly dense NYC airspace, it can create an emergency if you have to deviate that much.
The controller was harsh and made his frustration evident in the way he chose his words. The pilot stroked his ego by saying his boss would call the controller's boss.
Once you strip away the emotions, the pilot and controller did their jobs. The pilot kept his airplane clear of weather that he determined to be dangerous. The controller did the only thing he could to keep the Aer Lingus flight out of that weather and away from conflicting traffic.

P1 is no stranger to changeable weather & likely considered the clearance reasonable before takeoff.The controller should not suggest that P1 override judgement because 'someone else did it'. Conditions change rapidly. Both the controller & P1 should have kept the unnecessary conversation until later.

@copper.hat What is P1?

It means pilot in command. Sometimes appears in log books to designate role in flight. Incidentally, the pilot did not demand 15 miles, it was a response to ATC's question.

He says he needs 15 miles of runway heading at 0:36. https://youtu.be/w1r3XZQc4Zo?t=36

The controller didn't overstep their boundary but used poor judgment in using "another aircraft just did it..." as justification. That is almost always the last words of a crash as unforeseen weather tempted an aircrew to sneak in one more landing or takeoff. Fast cold fronts travel 1/2mi a minute and what the previous aircraft encountered has nothing to do with what is about to happen.
In the Pan Am Flight 759 with 153 people killed during takoff, The weather chart reported. "No fronts or low pressure areas were within 100 nm of the airport, and there were no severe weather warnings for the time and area of the accident"
The lemming principle of the guy in front of me seems to have lived, why not do it too - costs many lives. Good pilots don't wait until things are proven bad before they don't do them, they wisely refuse if it may be bad.
The pilot only had seconds after takeoff to assess the request. His assessment may or may not have been correct but he did not have the luxury of sitting at a desk for the last hour watching it evolve.
The previous Delta departure also saw something they did not like. The situation easily fits what may have appeared like (or even been) a micro burst forming. Something that could be new, it would not have effected the previous aircraft, and may not have been apparent to the controller, but would legitimately put safety in jeopardy.

PIC is the ultimate authority and can either accept or reject ATC instructions if unable to comply.  ATC was not wrong in that their job is traffic separation but they also pass on pilot reports to other aircraft operating in the area, so I can understand what they were trying to relay to the crew.  "However", with statement #1 above in mind, I would not let ATC vector me into a cell, having personally experienced a CB from the inside due to the under-whelming performance of a very old monochrome green weather radar unit and a captain who believed far too much in the radar's capabilities.  The pilot in the Aer Lingus example can try for a wider block of airspace and altitude to maneuver, but pretty unlikely near JFK (but you can still ask).


text:
Does this chart show a heliport in class D airspace without a control tower?
I was looking at the Los Angeles area on sky vector, and I noticed a tiny little triangular class D area right next to LAX. It shows that the height of the class D goes up to 2,500, but I couldn't see an airport in there, not even on the TAC.
Only if you click on "LA West Heli" on the top right on sky vector can you see that there is a heliport in that little area called "Chevron Refinery". On airnav, it says the identifier is 4CA6, and it says it does not have a control tower.
I have so many questions. Why is it class D if it has no control tower? Can a heliport even be class D? Why the actual heliport not appear on the sectional or even TAC? Can someone help me? :)

I think this may have been addressed before on ASE-- hang on, looking--

Actually the class D is for the nearby hang gliding airport.  (Kidding).  The existence of a marked hang gliding site in Class D is rather "interesting", considering the language of Part 103.  I know it's basically a "bunny hill" training site and they never get more than a few wingspans high there.  I wonder if any special arrangements were made re permission for hang gliding, when the airspace was given the Class D designation?  Could be grounds for another ASE question there--

These links re a related question appear to also answer your question -- https://aviation.stackexchange.com/q/50109/34686, https://aviation.stackexchange.com/a/82909/34686 . Basically, the Class D airspace is controlled by LAX tower, not the heliport. It's possible that the Class D airspace designation would have still occurred even if the heliport were not there--see the similar chunk of Class D airspace a few miles to the north, which contains no heliport or airport.

thanks @quietflyer
What is the purpose of this class D airspace if it contains no airport?

Well, it's in a high-traffic area close to LAX.  The fine print in the lower right hand portion of the text associated with the second link in the comment above, mentions a mid-air collision (elsewhere) which heightened concerns about airspace near busy airports -- and also indicates that the intent was to make the airspace Class B eventually. Apparently it was easier to make it Class D first.

@StephenS -- the last part of yellow-highlighted text in this answer https://aviation.stackexchange.com/questions/50109/when-is-this-class-d-airspace-not-class-d-airspace/82909#82909 indicates that the intent is to make the airspace at LAX part of the Class B eventually-- as far as SEA goes, I'm not seeing new expansions to the class D there-- it seems all the Class D near SEA is actually associated w/ KRNT and KBFI as described on pp D-71 and D-72 here -- https://www.faa.gov/documentLibrary/media/Order/order_7400.11E_2020.pdf -- last changed in '94-- or are you seeing something else?

@StephenS -- (continuing) -- I looked at https://www.faa.gov/air_traffic/publications/airspace_amendments/ and didn't see anything new near SEA --

@StephenS-- oops I forgot about my own ASE answer re SEA https://aviation.stackexchange.com/a/75354/34686.  Here the Class D is designated as an "extension".  Last modified '94. It appears on pp D164-165 of the current document https://www.faa.gov/documentLibrary/media/Order/order_7400.11E_2020.pdf.  Why they made it an "extension" here and not at LAX, who knows-- maybe they decided Class D "extensions" don't really fit the established pattern and shouldn't really exist.  Since the Class D at SEA has been there since '94, it doesn't look like they intend to ever convert it to part of the Cl. B

@StephenS -- re the "extension" question-- I guess part of the answer is contained in https://aviation.stackexchange.com/a/75354/34686 -- "Each piece of Class D airspace at KLAX is described as part of a ring of Class D airspace that completely encircles KLAX. "  So that's why it's not an "extension", because it is described in such a way that it includes the airport itself.  It just happens to be superseded by the Class B almost everywhere, so only two slivers are left.  But as to why they did it that way at LAX and not at SEA, who knows...

The triangular area you’re referring to is actually the LAX class D airspace.
The heliport itself is uncontrolled. It is not that uncommon for an uncontrolled heliport or airport to be within the surface area of a controlled airport. Departing aircraft are required to contact tower as soon as practical after takeoff, and arriving aircraft are told that landing is at their own risk.

Related: https://aviation.stackexchange.com/a/75354/34686


text:
Why does Schiphol Airport have such a long taxi?
I recently flew into Schiphol and experienced a very long taxi time (about 20 minutes) from landing to pulling into the pier at the terminal. Given that the flight was only 90 minutes from closing air plane doors to opening air plane doors. I feel that over 20% of flight time is a little excessive for taxiing at the destination airport.
I landed in the early evening. Around 19:30 local time with KLM.
Looking at a map I think I landed at Polderbaan runway as we crossed a main highway. Possibly the A5.

My question is: Why does Schiphol build a runway so remote when there is clearly available land nearer to the main airport terminal? And should this runway be used by short haul flights. Should it not be kept for long haul as it is the widest and longest runway at Schiphol?

Such long taxi stretches are very common at Schiphol, even with KLM. I myself experienced it.

Taxi time in Schiphol is often very long, always has been since I use the airport. It happens for short-haul flights, for long-haul flights, for low-cost flights, for KLM, for non-native airlines, it does not matter. But I don't think the question is a good one, it just invites speculation about policy decisions rather than a specific travel-related question.

The airlines at AMS have no say about which runway they're assigned for a flight. So they can't elect to avoid one or the other. If they could, all of them would elect to use 06-24 always, as it has the shortest taxi times. Taxi times to the 01R-36L can be as long as half an hour, depending on whether the 01C-36C is in use or not (if it isn't, it can be crossed at the halfway point, leading to a reduction in taxi time).

I last flew in to Schipol accompanied by a pilot used to flying there himself. When he saw our approach path he comment "Check out the length of the taxi when we land".

The last time I flew into Schiphol the captain got on the PA after landing to announce 'Welcome to the Netherlands. We will now be continuing our journey to Schiphol airport by road'

It's to avoid the SFO problem, where you can't use parallel runways in foul weather because they are too close together to be able to use instrument separation.  On the upside, taxis at SFO are short...

Schiphol indeed seems to have enough space to build a runway close to the terminal. However it is more the lack of airspace and laws preventing excessive sound levels that made it necessary to create the "polderbaan". It is also one of the two primary runways for nightflights (link in Dutch (sorry). Found a reference in the English wikipedia:

Newest runway, opened 2003.
  Located to reduce the noise impact on the surrounding population; aircraft have a lengthy 15-minute taxi to and from the Terminal.

This. Schiphol is in the middle of a very urban area, they have to spread out the flights. One day we'll be able to taxi to other airports, I think...

the map also doesn't tell the entire story. There's a drainage canal running in the area, and if I remember correctly some buildings (old farms) with monument status as well.

In addition to the noise issue mentioned in andra's answer, the Polderbaan (36L/18R,) Zwanenburgbaan (36C/18C,) and Aalsmeerbaan (36R/18L) runways are parallel. For parallel runways to be used simultaneously (especially if they can all be used for simultaneous arrivals or all used for simultaneous departures,) then there must be a minimum amount of separation between them in order to maintain the required horizontal separation between the air traffic. This may also be part of why the 36L/18R runway is so far away horizontally. An additional factor in the taxi time is that traffic going to or from the 36L/18R runway must taxi around the 36C/18C runway if it is being actively used for an arrival or departure.
As far as runways being 'reserved,' most airports don't reserve particular runways for long-haul flights. They may be given preference on a particular runway if it's needed, but that's unlikely to often be the case here, as all three of the parallel runways at Schiphol are sufficiently long for almost any passenger aircraft (they're all over 10,000 ft.)[1] In cases of parallel runways that are all sufficiently long, arrival runways are usually assigned more on a basis of which direction the traffic is arriving from than anything else. Which part of the airport the traffic will be taxiing to and how long of a line there is for each runway also may factor into the decision.

The required separation for parallel operations is much less than the distance to the Polderbaan: it's a couple of hundred meters, at most, whereas the Polderbaan is two kilometers from the next runway.

@David http://www.uecna.eu/spip.php?page=article&id_article=16 The separation between parallel runways in independant mode is 1,035m.

@DavidRicherby the actual distance is worse than the mere separation because of the roundabout taxiways that have to curve around other runways, parallel a major highway, and weave around a drainage canal and some farms.

@DavidRicherby, That's only true if one is being used for arrivals and the other for departures (for instance, within each pair of runways at ATL.) As SentryRaven pointed out, the separation requirements are much larger when the runways are being used for parallel arrivals or parallel departures. It gets even more tricky when you have 3 (or more) parallel runways that are all being used for simultaneous arrivals or all being used for simultaneous departures. I'm not sure if Schiphol ever does that, though.

@reirab never seen them use more than 2 of them at a time. The main purpose of building it was noise abatement, allowing the eventual (planned) closing of one other runway that can't be used effectively due to noise regulations (which have become so strict over the years that a few years ago it took a direct order from the ministry of transportation, temporarilly lifting the limits, overruling local city council imposed restrictions, to keep the airport open for the last 2 weeks of the year, they'd literally run out of allowed departures and arrivals).

Moving the runway further away gives Schiphol the chance to build an extra set of terminals which could connect to the main road. Also, land in Holland is expensive and noise pollution rules are strict, so it was best to build anything new in the middle of a field (an aerial view will show this).

Thats one way of ensuring you have space for expansion. If you don't build there someone will.


text:
What is the minimum altitude over Egmond aan Zee when landing at Schiphol?
I live in Egmond aan Zee which is about 36 km flight distance from Schiphol.
It seems that aircraft fly over Egmond when there is a southerly wind so they can make a landing approach to Polderbaan runway.
Where can I find the minimum allowed altitude when flying over Egmond?

By the way, do you mean southerly winds? When winds are from the North, planes would not land on 18R, but instead depart on 36L and possibly overfly Egmond while climbing.

Yes, I think you are correct-thankyou.

@Bianfable: And land on 36L, as well, for the same reasons.

@Sean, runway 36L is only used for takeoff and 18R only used for landing because the Polderbaan is so far away as it is and the far end (which does not even have taxi ways to it) would be even farther away.

The answers are all explaining at what altitude the planes should be based on the approach procedures. But be aware that the law is less restrictive: To be legal they must be 1000ft above the highest obstacle in built-up areas (which Egmond is), except for take-off and landing, then there is no minimum altitude. So it's not illegal to be at for example 1500ft over Egmond, just uncommon.

Approaches into Schiphol are usually vectored by ATC during the day (see below for night operations). This means the controllers are giving instructions to pilots depending on the current traffic, which makes it hard to say when exactly planes will overfly Egmond aan Zee.
If the Polderbaan (runway 18R/36L) is used for landing from the North (18R), planes will be vectored to the PEVOS waypoint shown on the following chart (source: Jeppesen):

At this waypoint, the aircraft should be at an altitude of 2000 ft (about 600 m):

I marked the approximate position of Egmond aan Zee on the map. There is no given minimum altitude there, so planes could already be at 2000ft, but they are likely still higher (3000 to 4000 ft) see below for update.
During night operations, Schiphol is a lot stricter about where planes can fly and how they can descent. The following night approach chart shows how planes will fly if they land on 18R:

Egmond aan Zee is between EH602 (where planes will be at FL70 or about 2100 m) and EH607, which is on a dashed line indicating a continuous descent path, where planes must fly at idle thrust from FL55 at NIRSI down to the ILS intercept altitude (2000 ft).

I just had a look at flightradar24.com and saw a KLM Boeing 737 flying quite close to Egmond:

According to the ADS-B data, they were between 1800 and 2000 ft when flying just south of Egmond an Zee (I marked the point where they leveled off at 1800 ft). I assume this data is somewhat inaccurate since they should not descent below 2000 ft before intercepting the ILS. Other aircraft were also at similar altitudes around Egmond, so I assume overflights at 2000 ft are quite common.

ATC may be allowed to vectors flights below 2000ft, so intercepting the ILS at 1800ft seems entirely plausible

@J.Hougaard That's interesting, I did not know that. MSA in that direction is 1700 ft, I guess they would not go below that...

The MRVA (minimum radar vectoring altitude) can be lower than MSA, because the two things are defined differently. Where I work, I will regularly vector aircraft onto an ILS at 1500ft (which is the MRVA in that sector), even though the published ILS procedure begins at 2000ft and the MSA in that area is 2300ft.

During normal daytime operations aircraft are passing over the southern edge of Egmond aan Zee at 2000 ft (600m) altitude. They maintain 2000 ft until estabilshed on the ILS to runway 18R (or 18C). The aircraft come from the south (e.g. Portugal, Spain, France, Belgium) or west (UK, Ireland, Iceland, transatlantic) and descent to 2000 ft over the north sea.
Aircraft turning onto final approach for 18R or 18C arriving from the east (rest of europe, asia, middle east, etc) are kept at 3000 ft. This way vertical separation is assured, even when aircraft overshoot their turn and get horizontally close to the traffic from the other side.